• Back to Encyclopedia Arctica homepage

    Algae: Planktonic Groups

    Encyclopedia Arctica 5: Plant Sciences (General)

    Algae: Planktonic Groups

    Unpaginated      |      Vol_V-0068                                                                                                                  
    EA-Plant Sciences

    (R. Ross)




    Bacillariophyceae 1
    Structure 1
    Reproduction 4
    Colony Formation 5
    Arctic Habitats 5
    Composition of Arctic Diatom Flora 9
    Dinophyceae 10
    Arctic Occurrence 14
    Chrysophyceae 15
    Arctic Occurrence 19
    Xanthophyceae 20
    Bibliography 23

    001      |      Vol_V-0069                                                                                                                  
    EA-Plant Sciences

    (R. Ross)





            The Bacillariophyceae or diatoms ( Bacillariophyta ) are a group of

    microscopic unicellular plants belonging to the Algae. Like almost all

    plants, they manufacture their own food from mineral salts, carbon dioxide,

    and water, using energy from sunlight absorbed by their green pigments.

    They occur in all waters, both fresh and salt, throughout the world and,

    except in tropical oceans, are among the predominant forms of plant life

    in regard to quantity. They are less affected by adverse conditions than

    higher plants, and some species can survive exposure to a temperature of

    -80°C. for long periods. Being unicellular, they can multiply rapidly as

    soon as the water they live in thaws. They are particularly abundant in

    arctic and Antarctic waters and form the starting point of the food chains

    which lead through the smaller marine animals — copepods, medusa, pteropods,

    etc. — to fishes, whales, and other marine mammals. The rich diatom popula–

    tion is the principal reason for the abundant life in arctic seas.



            Individual diatoms are one-called and vary in size from about 0.005

    millimeters long and about one-third as broad, to disks 2 millimeters in

    diameter, or rod-shaped forms 5 millimeters long. In the majority, however,

    the longest dimension is between 0.02 and 0.2 millimeters. Their chief

    002      |      Vol_V-0070                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

    distinguishing feature is that each cell has a boxlike siliceous exoskeleton

    known as the frustules. This consists of two halves fitting over each other

    like the top and bottom of a pillbox. Each half is normally made up of two

    parts, the valve, which forms the top or bottom of the box, and the girdle,

    which is the side. Although there is usually only one girdle attached to

    each valve, in some species the valves are separated by a number of complete

    or partial loops. Other species have perforate septa across the interior of

    the frustule in a plane parallel to the valve. There may be only two of

    these, one attached to each valve, or many which fit into each other.

            The frustules, especially its valves, is normally covered with regularly

    disposed fine markings in the form of dots, bars, or a honeycomb. These are

    cavities in the silica which are usually open on the inner side and closed

    by a fine membrane on the other side. This membrane itself often shows

    fine markings; whether or not it is perforate is still undecided in spite

    of investigations with the electron microscope.

            There is great variety in the shape of the frustule and in the dispose–

    tion and nature of the markings, and a full survey of the variations is

    beyond the scope of this account. Reference should be made to the works

    quoted in the bibliography for more detailed information than is given

    here. many diatoms have circular valves, flat, convex, or undulating, and

    have their markings arranged in a radial or concentric pattern. These,

    together with a number of elliptical, triangular, or polygonal forms with

    processes at their corners, comprise the order Centrales. In this order

    also is included the suborder Soleniineae whose long cylindrical frustules

    are usually very feebly silicified and have a complex connective zone

    consisting of many incomplete hoops; their valves are small and offen

    003      |      Vol_V-0071                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

    markedly excentric. They are all planktonic and the cells unite to form

    long chains, as they also do in another planktonic group, the family

    Chaetopceraceae, which are illiptical or circular forms with long awnlike


            In the order Pennales, which comprises the remainder of the diatoms,

    the markings of the valve are disposed about a longitudinal line and are

    thus more or less bilaterally symmetrical. This order, which is numerically

    larger than the Centrales, exhibits an even greater variety of shape and

    structure. The longitudinal axis may be straight, arcuate, biarcuate, or

    sigmoid, more or less median or markedly excentric, and is often raised on

    a keel. The outline of the valve varies from the linear to the arbicular

    and is sometimes cuneate.

            An organ known as the raphe occurs in some of the suborders of the

    Pennales. This is a cleft, often oblique or folded, through the silica of

    the valve, and normally lies in the longitudinal axis. It usually occurs in

    both valves of the frustule, but in one family the Achnanthaceae, it is found on

    only one valve. In two large families, the Bacillariaceae and the Surirellaceae,

    the raphe is on a keel and is of a rather different structure. It consists of

    a canal opening to the interior of the frustule by a series of pores and to

    the exterior by a fine oblique slit. Only those diatoms which possess a

    raphe can move, a fact which provides strong evidence for the view that their

    movement, a comparatively slow creeping motion, is due to the streaming of

    protoplasm along the raphe. Other theories, most notably the presence of

    cilia, are still put forward but seem less well founded.

            The cell content is much less variable than the frustules. On the

    inside of these is a lining of protoplasm which encloses one or two large

    004      |      Vol_V-0072                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

    vacuoles. The single nucleus occurs either in the bridge of protoplasm

    separating the two vacuoles or else in that lining the frustule. Each cell

    contains one to many olive-green bodies, the chromatophores. In [ ?] general,

    the Pennales posses large flat chromatophores, usually two in number, while

    the Centrales normally have numerous, small, lens-shaped ones. The olive–

    green color is due to the yellow pigments being present in greater propor–

    tion to the green than is the case in higher plants. The food reserves are

    normally stored as oil ad a few oil globules are usually present in the cell.



            This is normally by binary fission. When the cell divides, two nes

    valves are formed in the old frustule before the two halves of the old girdle

    separate. These new valves, with their girdles, form the inner halves of the

    new frustules and, since they cannot grow after they are formed, one daughter

    cell is the same size as the parent while the other is slightly smalle d r .

    Growth of the cell between divisions takes place by the two valves moving

    farther apart. Repeated divisions accordingly reduce the average size of

    the individuals in the population and if may fall to one-quarter of its

    original figure.

            The original size is restored by a different type of reproduction, known

    as auxospore formation, in which the cell contents emerge from the frustule

    and new large-size individuals are formed. This is a sexual form of repro–

    duction. Typically two individuals come together and, after a reduction

    division, one, two, or four gametes are formed in each cell. These gametes

    fuse in pairs, one from each cell, and the resulting zygotes grow rapidly

    and form the auxospores, which lay down new, larger frustules about themselves.

    005      |      Vol_V-0073                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

    Apogamy, in which after the reduction division two nuclei from the same

    cell fuse to form the zygote, occurs in some Pennales and is the rule in

    the Centrales.

            Some planktonic species of diatoms form resting spores. The cell

    contents contract away from the valves at the onset of unfavorable conditions

    and lay down a thick-walled siliceous endocyst around themselves. This does

    not resemble the normal frustule of the species; it has no fine markings and

    usually bears spines. These resting spores survive the unfavorable period

    and germinate, producing cells with normal valves, when favorable conditions



    Colony Formation

            Most diatoms live free and solitary lives but some attach themselves

    to the substratum by secreting a gelatinous pad or stalk. In some such

    forms this attachment forks when cells divide, and a colony on a much-branched

    stipe results. Some raphe-bearing species form long, branched, gelatinous

    tubes in which the frustules live. A more frequent type of colony is a

    filament formed by the failure of the daughter cells to separate after cell

    division. These are sometimes attached to a substratum by their terminal

    frustule, or they may occur free. Many planktonic species form such chains;

    others form colonies consisting of a number of cells embedded in a common

    mucilaginous envelope.


    Arctic Habitats

            In both fresh waters and the sea, there are two ecological groups of

    diatoms - those which live on substratum, and the free-floating plankton.

    In fresh waters, where their growth begins again each summer as the ice and

    006      |      Vol_V-0074                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

    and snow melt, diatoms form an olive-green to gray-green flocculent layer on

    the bottom and on submerged plants, etc. in sunlight, photosynthesis is

    often so active that bubbles of free oxygen are formed which, becoming en–

    tangled in this layer, carry lumps of it to the surface. All except the

    smallest bodies of water have their planktonic diatom flora, but little is

    known of the plankton of any arctic lakes. The growth of diatoms, both

    planktonic and bottom-living, is limited to depths shallow enough to permit

    the penetration of enough light for photosynthesis. This limit depends on

    the clearness of the water and varies from a few feet to more than fifty.

            Diatoms not only occur in practically all permanent bodies of water but

    also in puddles, in which they grow rapidly, and in any damp places, such as

    tufts of moss where they are found in quantity. Soils in temperate regions

    usually have a considerable population of diatoms, mostly very small forms.

    The presence of a well-developed diatom flora in Icelandic soils indicates the

    strong probability that one will be found also in the Arctic.

            In general, arctic freshwater diatoms are smaller and have finer markings

    than those of more temperate waters. Individuals from arctic localities are

    not smaller a than those of the same species from farther south, but the

    smaller and more finely marked species tend to extend farther north than the

    larger and coarser ones. This appears to be a temperature effect, since

    shallow waters well warmed by the sun contain larger and coarser forms than

    are found in colde d r waters in the same district. However, the chemical

    content of the water, in particular the pH and salinity, is often the

    principal factor determining the diatom flora, diatoms being scarce in

    acid waters poor in mineral salts, and frequent in waters of higher pH and

    salt content.

    007      |      Vol_V-0075                                                                                                                  
    EA-PS. Ross: [ ?] Algae: Planktonic Groups

            Marine . Marine diatoms are plentiful along those arctic shores which

    are free from ice in the summer months, growing on the larger algae, on

    mollusk shells, stones, etc., and living free on the bottom in shallow

    water, on the shore between tidemarks, and in rock pools — as in temperate

    waters. In the Arctic, in addition, the ice floes support a large diatom

    population containing many species not found elsewhere.

            Diatoms begin to grow on the ice about March. They grow on the

    undersurfaces and sides of the floes, particularly on the ice foot, and in

    pools in the surface of the floes. There they form small, round patches and,

    since these, being dark-colored, absorb more solar energy than the surrounding

    ice, they raise the temperature locally and melt the ice on which they are

    growing. In this way the ice becomes pitted with holes giving rise to the

    condition known as “rotten ice” by the early whalers. Among diatoms from

    ponds on the ice, some freshwater species, and also the spores of marine

    planktonic species, are often found. The spores are formed in the autumn

    and incorporated in the ice as it freezes. The freshwater forms are not

    found in large numbers and have only been seen in acid-cleaned preparations.

    It is accordingly not known whether they were living on the ice, and indeed

    it has been generally assumed that they were dead frustules, either blown

    there or present because the ice had formed in a river estuary. The water

    in the pools is often almost fresh, however, and the frequency of their

    occurrence suggests that they may be able to maintain themselves there for

    a time.

            In those parts of the Arctic Sea which are not ice-free during the

    summer, there is little true phytoplankton. However, in the leads between

    the floes, globular aggregations of littoral diatoms, often as large as a

    008      |      Vol_V-0076                                                                                                                  
    EA-PS. Ross: Bacillariophycease

    man’s fist, are found. These lumps, often present in large numbers, contain

    species of other algal groups as well as [ ?] most of the diatoms found on

    the neighboring ice, and they apparently originate from the film of diatoms

    on the ice. They congregate at the interface between the salt and fresher

    water which is formed one or two feet below the surface as the ice melts.

    The sudden change of salinity encountered there result in the death of their

    outer layers which become bleached in the later part of the summer.

            With the onset of winter and littoral diatoms of the ice fields and most

    of those growing along the coasts become embedded in the newly formed ice.

    All the species are able to survive this, although the majority of individuals

    succumb. The survivors produce the next season’s crop when light and warmth

    return in the spring.

            The planktonic diatoms fall into two groups. There are the truly oceanic

    types which maintain themselves in open water throughout the year. Most of

    these are discoid forms or species of the genus Chaetoceros . The Soleniineae,

    which are prominent in the plankton of most seas, are comparatively rare in

    arctic waters, although a few species are carried by Atlantic water into the

    Greenland and Barents seas. The other group are the neritic types, which are

    incapable of passing the whole year in the plankton and are only found in

    coastal waters or near the ice fields. In some it is only the resting spores

    which are not planktonic, but others, e.g., Melosire arctica , probably the

    commonest arctic diatom, can flourish either on the ice or in the plankton.

    A fuller account of the arctic phytoplankton will be found in the article


    009      |      Vol_V-0077                                                                                                                  
    EA-PS. Ross: Bacillariophycease Algae: Planktonic Groups


    Composition of Arctic Diatom Flora

            The freshwater diatom flora of the Arctic contains few species

    peculiar to the region but consists largely of forms also common in

    temperate lands. Many found in warmer climates, however, are unable to

    withstand arctic conditions and hence the arctic diatom flora is less varied

    than that of countries farther south. It is nevertheless quite extensive,

    and more than 500 species of freshwater diatoms have been recorded from north

    of the Arctic Circle. The freshwater diatom flora of Ellesmere Island, our

    present knowledge of which is based on only six gatherings, illustrates

    these points. From these 72 species are known, of which 14 are confined

    to the Arctic and Subarctic and 7 more elsewhere only occur in alpine habitats.

    The remaining 70% of the freshwater diatoms from this island, which lies north

    of latitude 75° N., are temperate species. Most diatoms found only in the

    Arctic have a circumpolar distribution. Although many species have wide

    ranges, the freshwater species peculiar to the Arctic [ ?] have not been found in

    the Antarctic.

            The marine diatoms present a different picture. The location and move–

    ment of the principal water messes control the distribution of planktonic

    forms; hence the plankton characteristic of the cold arctic water is not

    normally found outside high latitudes, except when carried southward by

    such surface currents as the Labrador Current. Similarly the plankton diatoms

    of temperate waters are carried into the Greenland and Barents seas by the

    Gulf Stream. Many arctic marine plankton species are also found in the


            While the diatoms found along the coasts of the Arctic Sea include many

    temperate species, most of those found on the ice floes do not occur outside

    010      |      Vol_V-0078                                                                                                                  
    EA-PS. Ross: Bacillariophycease

    the Arctic. Again, while some of these forms occur throughout the Arctic

    Sea, many have been reported only from the region of the great polar drift

    from the Bering Strait westward to northeast Greenland, which accordingly has

    a richer flora than is found elsewhere. Physical and chemical conditions,

    particularly the latter, seem to be the main factors in determining the

    distribution of diatoms, and the low and varying salinities of the surface

    waters in the ice fields are not encountered in more temperate seas. It is,

    therefore, not surprising that the diatoms found there are peculiar to that

    habitat. Similar conditions are, however, encountered in the Antarctic but

    the flora there is different, and very few species are common to the ice of

    both polar regions.



            The Dinophyceae, often referred to as the dinoflagellates or peridinians,

    are a class of Algae which are generally unicellular, although a few filamen–

    tous forms occur. The majority of them are found in the plankton, either of

    the sea or of fresh waters, and they constitute one of the most important

    elements of the phytoplankton. While typically they are pigmented forms with

    holophytic nutrition, there are a considerable number which are colorless and

    holozoic or parasitic.

            The unicellular forms are characterized by the presence of two flagella,

    one of which is directed transversely and often encircles the cell more or

    less completely, while the other is directed longitudinally. In most genera

    these flagella are inserted on the side of the cell and lie in furrows, one

    of which, containing the transverse flagellum, encircles the cell and is often

    termed the girdle. The longitudinal flagellum is normally directed backward,

    011      |      Vol_V-0079                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    and hence the longitudinal furrow is found on the part of the cell behind the

    girdle, although it sometimes continues forward toward the apex. Both flagella

    are used for progression, their undulating movements propelling the organism

    forward with a rotating motion.

            The chromatophores of the colored forms are usually numerous and disk–

    shaped, and dark yellow or brown owing to the presence of carotinoid pigments —

    particularly the dark red peridinin, in addition to the green chlorophyll.

    These chromatophores lie in the outer part of the cell where the protoplasm

    is dense and granular. The inner part of the cell is occupied by the large

    nucleus and by one or more vacuoles filled with a sap which is normally rose–

    or calmon-colored. These vacuoles have a well-defined membran c e and definite,

    often spherical, shape. Their function is probably excretory. The majority

    of the genera possess of a cell wall consisting of cellulose, which often is

    very complex and composed of many plates.

            The simplest and most primitive members of the Dinophyceae belong to the

    subclass Desmokontae. In many of these the flagella are inserted at the apex

    of the cell and there is no transverse, and frequently no longitudinal, furrow.

    These are the only members of the class in which the longitudinal flagellum

    is directed forward: they include some without a cellulose wall. In others

    of this subclass the two flagella emerge from a single pore on the side of

    the cell and both lie in furrows, the margins of which are often expanded

    into wings. When these wings are well developed, the cell wall can have a

    very complex shape, but it never consists of more than two portions joined

    by a longitudinal suture.

            Reproduction is by longitudinal division and one half of the cell wall

    goes to each daughter cell, which lays down a new second half. This subclass

    012      |      Vol_V-0080                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    is represented in the marine phytoplankton of the Arctic by a number of species

    of Exuviaella and Dinophysis , both genera with a cellulose cell wall. In

    Exuviaella the flagella are apical, but in Dinophysis they are inserted

    ventrally and lie in transverse and longitudinal furrows, respectively.

            The simples members of the remaining subclass, the Dinokontae, also

    have no cellulose cell wall. In all of them, however, the flagella emerge

    separately on the ventral side; and they all have well-marked transverse and

    longitudinal furrows in which these flagella lie. Some of these forms have

    chromatophores and are holophytic. Others are colorless and holozoic, ingest–

    ing small particles of food by means of pseudopodia protruded from the antapical

    part of the cell near the longitudinal furrow. Both holophytic and holozoic

    species of this type are found in the phytoplankton of the Arctic, the genus

    Gymnodinium being the best represented.

            Closely related to these are a number of forms which live as parasites,

    mostly on various types of animals, of which planktonic copepods are the

    favorites. In the parasitic stage they occur as unicellular cystlike

    organisms either in the tissues of their host or externally, and show little

    evidence of being Dinophyceae. Their affinities are revealed, however, by

    the structure of the motile swarmers which they form from time to time. These

    resemble the simpler members of the Dinokontae which have no cellulose cell

    wall. One of this group occurs as a parasite on marine planktonic diatoms

    of the genus Chaetoceros , and has been recorded from the waters around


            Most members of this subclass are forms with a definite cellulose cell

    wall. This consists of a girdle forming the furrow in which the transverse

    flagellum lies, and a series of unequal polygonal plates, the number and

    013      |      Vol_V-0081                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    and arrangement of which differs from species to species. These plates have

    knifelike margins and are firmly cemented together. They are usually pierced

    by pores, which frequently lie in the center of the areolations with which

    the plates of many species are ornamented. The shape of these armored

    Dinokontae varies greatly. Peridinium, one of the commonest genera in the

    sea and fresh waters in the Arctic, is subspherical, with an [ ?] indentation

    in the region of the longitudinal furrow and sometimes two small horns or

    spines at the antapical end. Goniaulax, another frequent arctic genus, is

    very similar and only differs in the detailed arrangement of the plates. In

    Ceratium , another common marine genus, there is one long apical horn an two

    or three antapical horns of varying length, which may be bent sideways or

    forward. The length of these horns in proportion to the size of the body

    tends to be greater in tropical species of the genus than in those inhabiting

    colder water, a fact shich is presumably correlated with the lesser density

    of warmer water and the consequent need for more “form resistance” therein.

    Almost all these armored forms are pigmented and holophytic.

            Reproduction in many species of Dinokontae is by binary fission during

    movement. The plane of division is oblique and one flagellum goes to each

    daughter cell, the other being regenerated. In some armored forms, including

    many species of Ceratium , the cell wall ruptures along a lone between definite

    plates. The exposed protoplast assumes the characteristic shape of the species

    and the remaining plates of the cell wall are gradually developed. In others,

    including Peridinium spp., there is no split but the new envelopes grow over

    the surface of the daughter cells as they divide. In many other species

    division occurs in a sedentary phase. The protoplast contrasts away from

    the cell wall and divides obliquely in its contracted state. This division

    014      |      Vol_V-0082                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    may occur before or after liberation from the old cell wall, which ruptures

    to allow its contents to escape. In some cases the contracted protoplast

    develops a new membrane before liberation from the parental one. The thin–

    walled spherical cysts so formed may act as a resting stage of some duration,

    but usually under favorable conditions they divide at once. These cysts

    differ considerably from the thick-walled resting spores with ample food

    reserves which are known in a number of armored freshwater species. These

    are the means by which they survive unfavorable climatic periods. When they

    germinate, the young individual which emerges from the ruptured cyst resembles

    the unarmored members of the subclass, but in time grows a typical cellulose

    envelope. Sexual reproduction in this group has never been observed, although

    it is suspected to occur in some forms where unusually small unarmored swarmers

    have been seen and interpreted as gametes.

            In addition to these flagellate unicellular forms, there are a number of

    general of Dinophyceae which are normally nonmotile, existing either as single

    cells or as short filaments. Most of these reproduce by the liberation of

    biflagellate swarmers with one longitudinal and one transverse flagellum,

    and with evident furrows. No such forms have, however, yet been recorded

    from the Arctic.

            For a more detailed description of this class Fritsch (4) should be

    consulted. Lindemann (11) also gives a fairly full account, together with

    a synopsis of the genera and their characteristics, while Schiller (14)

    gives descriptions and keys of all the species.


    Arctic Occurrence

            The Dinophyceae are typically planktonic organisms. In the sea they

    015      |      Vol_V-0083                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    play an especially important part in oceanic waters and in the warmer regions,

    where they make up the bulk of the phytoplankton. In the Arctic they are

    less important than the diatoms, but they nevertheless constitute an appre–

    ciable part of the phytoplankton. In the spring, before the ice melts, some

    of the naked forms have been found along with other flagellates constituting

    a not very rich phytoplankton in the waters of the East Greenland current (2).

    Such a community is probably widespread at that time of year, but further

    observations are required before this can be established. This flagellate

    community is replaced by diatoms when the ice melts, and these are often

    found in great numbers. Their maximum is followed, when the water is warmer

    but less rich in mineral salts, by a phytoplankton dominated by armored

    Dinophyceae, members of the genera Ceratium and Peridinium being particularly

    prominent (2; 7). The parasitic species Paulsenella chaetoceratis is also

    found in the early summer plankton off Greenland on its host, the diatom

    genus Chaetoceros. It is to be expected that the species parasitic on

    zooplanktonic copepods, etc., will be found to be represented in the Arctic

    also. The total number of marine species so far recorded from the Arctic

    is about 200. More details of the part which the Dinophyceae play in

    marine phytoplankton will be found in the article “phytoplankton.”

            About 10 species of Dinophyceae have so far been recorded from arctic

    fresh waters (1; 15; 16), where they are apparently not a large component

    of the algal flora. Little is known of the conditions which favor their




            This class of Algae consists mainly of unicellular and colonial forms.

    016      |      Vol_V-0084                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    There are a few filamentous types known, but none of these have so far

    been recorded from the Arctic. The chromatophore o s f this class are brown

    or orange in color, owing to the presence of one or more accessory pigments.

    They are normally large, few in number, and parietal in position. The

    food reserves are stored as fat and as a substance known as “Leucosin”

    which occurs as opaque rounded masses of a whitish color and is thought to

    be a carbohydrate; starch does not occur. The protoplasm is always clear and

    free from granules. Another characteristic feature of this class is the

    formation of silicified cysts by its members. These cysts, which are formed

    within the cell, are approximately spherical in shape, with various ornamenta–

    tions on the surface, and with a pore closed by a cone-shaped, unsillicified


            There are a large number of motile unicellular flagellate members of this

    class, but very few have been reported from the Arctic. In view of the fact

    that in temperate regions the freshwater forms favor cold conditions, occurring

    most abundantly in the winter and in cold mountain waters, this might seem

    surprising were it not for the fact that most of them are so delicate as to

    lose all their distinguishing features on preservation. They [ ?] therefore

    need to be studied alive. Only two unicellular forms have so far been recorded

    from the Arctic. One is a species of the often colonial genus Dinobryon and

    will be described later. The other is chrysococcus rufescens , found by

    Shirshov (15) in Novaya Zemlya. In this latter the cell is enclosed within

    a rigid spherical envelope, leaving a pore through which the single flagellum

    passes. In age, the envelope becomes colored brown by iron salts. Repro–

    duction is by binary fission, one of the products escaping from the envelope

    as a naked swarmer and forming a new individual, the other being retained in

    the original envelope.

    017      |      Vol_V-0085                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

            Two groups of unicellular members of this class are recorded from the

    marine plankton of the Arctic. The Coccolithophoridadeae are represented

    by about 10 species. In this family the cells have an outer membrane,

    gelatinous at first if not later, in which a number of calcified inclusions,

    the coccoliths, are deposited. These vary in shape from genus to genus but

    are most frequently circular. They are often perforated in the center and

    may bear processes on their outer sides which stick out from the cell like

    stout spines. The gelatinous membrance of some species becomes calcified with

    age, so that the coccoliths become embedded in a rigid envelope. In this

    family there are normally two flagella and two thromatophores. In reproduction

    the flagella are withdrawn, the protoplasm contracts somewhat, and then divides.

    In some species the division in equal and both daughter protoplasts emerge from

    the parental envelope as naked swarmers; in others it is unequal, the larger

    protoplast remains within, and only the smaller one escapes.

            The Silicoflagellatae are only doubtfully referred to the class Chrysophyceae.

    They possess an internal skeleton made of siliceous rods. Their chromatophores

    are yellow or brownish-yellow, numerous, and discoid. Fat and leucosin are

    both stated to occur as assimilatory storage products. There is a single apical

    flagellum. Little is known of their life history, but reproduction appears to

    occur normally by binary fission. Resting stages with no flagellum and a

    distinct external membrane have been reported.

            Many of the flagellate Chrysophyceae are colonial, the cells being grouped

    in various ways. Three general reported from Arctic fresh waters, Synura,

    Chrysosphaerella , and Uroglena , have spherical colonies. In Synura and

    Chrysosphaerella the cells are closely packed. In the latter of these they

    are uniflagellate and on either side of the flagellum there is a small cup

    018      |      Vol_V-0086                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    from which a long, hollow, siliceous rod protrudes. There are also small

    siliceous scales in the mucilaginous envelope of the colony. In Synura

    the cells, each of which has two equal flagella, are united by the bases of

    their membranes and there is no mucilage envelope for the whole colony. The

    envelopes of the individual cells are tough and abovoid or ellipsoid in

    shape. Uroglena has the cells at the surface of a large, roughly spherical

    mass of mucus, and they are usually well separated. In all of these genera

    the cells have two chromatophores. In none of them is the number of cells

    in the colony definite, division of individual cells going on continuously.

    Reproduction may occur by division of the whole colony or by the liberation

    of swarmers.

            Dendroid as well as spherical colonies are found in this class of Algae.

    In the genus Dinobryon the individual cells each possess an envelope with a

    wide mouth and a pointed base. The two flagella of each cell are unequal.

    Some species are solitary and one such has been recorded from the fresh waters

    of Greenland. This reproduces by longitudinal fission, one of the daughter

    cells escaping from the envelope and forming a new individual. In other

    species, after longitudinal division one daughter cell migrates until it

    is attached by its base close to the opening of the parental envelope. It

    there lays down a new cellular envelope. Branched colonies are thus formed

    which differ in shape according to the frequency and sequence of the divisions.

    New colonies are formed by the liberation of swarmers, either after longitu–

    dinal division of a cell or by the escape of its whole protoplast. In one

    case fusion of swarmers formed by longitudinal division has been observed.

    Spherical cysts with a short projection on one side are formed just outside

    the cellular envelope in many species. The species concerned pass through

    019      |      Vol_V-0087                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    By means of these, the species concerned pass through unfavorable climatic


            Some members of this class are normally amoeboid in structure and holo–

    zoic in nutrition, revealing their relationships only when they produce

    swarmers of typical chrysophycean structure. None of these is recorded from

    the Arctic. In other forms the normal state is a palmelloid one, concisting

    of large numbers of rounded cells embedded in mucilage. The marine planktonic

    Phaeocystis has large mucilaginous colonies with spherical lobes, in the surface

    of which are embedded rounded cells with two yellowish [ ?] chromatophores.

    This type reproduces both by detachment of lobes and by the liberation of

    swarmers with two unequal flagella. Another palmelloid dorm is Hydrurus foetidus,

    which occurs in running water and has been reported from Greenland. It forms

    tufts of touch mucilaginous strands in which the cells are embedded. In each

    branch there is an apical cell which divides repeatedly. The cells are

    initially spherical in shape but become drawn out and pear-shaped with age.

    Reproduction is normally by swarmers which are formed on short side branches

    by the longitudinal division of a series of cells. In summer some cells are

    protruded in mucilaginous projections from the surface of the thallus and these

    form silicified cysts with a broad, delicate wing extending around half the


            Fuller accounts of the morphology and life-history of this class of Algae

    will be found in Pascher (12) and Fritsch (4).


    Arctic Occurrence

            Both Coccolithophoridaceae and Silicoflagellatae are characteristic of

    temperate and tropical oceanic water, and they are only found within the

    Arctic where the currents bring in such waters. One silicoflagellate,

    020      |      Vol_V-0088                                                                                                                  
    EA-PS. Ross; Algae: Planktonic Groups

    Distephanus speculum, is, however, comparatively abundant along the coast of

    Greenland in the summer (1; 7). Phaeocystis pouchetii is found associated

    with diatoms in their spring maximum towards the southern limits of the Arctic

    area in the Atlantic (7), although it also is typically a temperate form.

    Dinobryon pellucidum , on the other hand, is widely distributed in the Greenland

    sea, Davis Strait, and Baffin Bay.

            The freshwater Dinobryon bavaricum var. vanhoeffenii was the dominant

    member of the phytoplankton of the lake near Karajak Fjord in West Greenland

    investigated by Vanhoeffen (16). Other freshwater members of this class have

    been listed as occurring in various localities in Greenland (1), Novaya Zemlya,

    and Franz Josef Land (15), and, though few in number of species, are apparently

    often prominent members of the algal population.



            This class of Algae, which is also known as the Heterokontae , is small

    in numbers and sparsely represented in the Arctic by about 10 species, of

    which one, Halosphaera viridis , is a marine planktonic form; the others

    inhabit fresh water. Within the class there are to be found motile flagellate

    forms, unicellular and colonial nonmotile forms, filamentous forms, and

    siphoneous types. Within each type of group of forms, however, there is

    little range of variation. The chromatophores are usually numerous and dis–

    coid, and are of a yellowish-green color owing to the presence of an excess

    of xanthophyll. Starch is absent, and oil is the usual food reserve. The

    cell wall, when present, is rich in pectic substances and often consists of

    two overlapping parts. The motile cells have two apically inserted flagella

    of very unequal lengths. The longer of these is complex in structure, with

    021      |      Vol_V-0089                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    many fine side branches.

            In all the forms of this class so far reported from the Arctic, the

    motile phase occurs only temporarily in reproduction. Halosphaera viridis

    has large spherical cells, most of the interior of each being occupied by a

    central vacuole. The chromatophores are numerous, flattened, and somewhat

    angular. The pectic cell wall is slightly silicified and consists of two

    equal halves joined at their margins. As the cells grows, the membran c e is

    burst open and a new one is laid down. Reproduction is by swarmers with

    two chloroplasts, and an oval or spherical shape. This species is common

    in Gulf Stream waters and is found wherever these penetrate into the Arctic,

    spreading farther as the summer advances. There is some indication that it

    maintains itself throughout the year in the open water of the Barents Sea (18).

            Characiopsis is a unicellular epiphytic form from fresh water and has

    been found in Franz Josef Land (15). The cell membrane is in two unequal

    parts and is attached by a mucilaginous cushion at the foot of a stalk. The

    mature cells are often multinucleate, and zoospores are formed by the proto–

    plasm rounding off the smaller, upper part of the cell membrane.

            Ophiocytium recorded from Greenland (1) and Baffin Island (17), is

    another genus which is primarily epiphytic. It is invariably multinucleate

    and has the form of an elongate cylinder. The cell wall is of two unequal

    parts of which the larger consists of a series of long thimble-like strata

    with expanded margins. The other part fits over this like a lid, and becomes

    detached when the reproductive bodies, which may be flagellate zoospores or

    nonmotile aplanospores, are liberated. The three species recorded from the

    Arctic are not normally epiphytic.

            Mischococcus confervicola , which has also been reported from Franz Josef

    022      |      Vol_V-0090                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups

    Land by Shirshov (15), is another epiphytic form. It consists of colonies

    of rounded cells borne at the tips of more or less regularly forked mucilage

    stalks. The cells contain two chromatophores. Reproduction is by unflagellate

    motile spores which are formed singly or in pairs within the cells. Nonmotile

    aplanospores are also frequently formed.

            In the genus Tribonema , which has been reported from Greenland (1), Novaya

    Zemlya, and Franz Josef Land (15), the alga consists of unbranched filaments.

    The cells are usually uninucleate and have a number of discoid parietal chromato–

    phores. A sexual reproduction is by zoospores with two unequal flagella. These

    are formed singly or in pairs in the cells. Nonmotile thick-walled aplanospores

    are also known. These may form new filaments which they germinate, or they may

    liberate one or two flagellate spores. Isogamous sexual reproduction has been

    observed once. Occasionally Tribonema secretes irregular masses of mucilage

    around its filaments and these become impregnated by ferric carbonate deposited

    by bacteria which are thought to be symbiotic with the alga.

            Fuller accounts of the morphology and life history of this class will be

    found in Fritsch (4) and Pascher (12).

    023      |      Vol_V-0091                                                                                                                  
    EA-PS. Ross: Algae: Planktonic Groups


    1. Bachmann, H. “Beiträge zur Algenflora des Süsswassers von Westgrönland.”

    Mitt.Naturf.Ges.Luzern , vol.8, pp.1-181, 1921.

    2. Braarud, T. “The ‘Øst’ expedition to the Denmark Strait, 1929.” II. The

    phytoplankton and its conditions of growth,” Hvalråd.Skr.

    vol.10, pp.1-173, 1935.

    3. Brown, R. “On the nature of the discolouration of the Arctic Seas,”

    Bot.Soc.Edinb. Trans. vol.9, pp.244-52, 1868.

    4. Fritsch, F.E. The Structure and Reproduction of the Algae . Cambridge,

    England. The University Press, 1935. Vol.1.

    5. Gran, H.H. Diatomaceae from the Ice-Floes and Plankton of the Arctic

    Ocean. London, N.Y., Longmans, Green, 1904. Norwegian North

    Polar Expedition, 1893-1896. Scientific Results no.11.

    6. ----. “Die Diatomeen der Arktischen Meere,” Römer, and Schaudinn.

    Fauna Arctica. Jena, 1904. Vol.3.

    7. Grontved, J., and Seidenfaden, G. “The Phytoplankton of the waters west

    of Greenland.” Medd.Grønland , vol.82, no.5, pp.1-380, 1938.

    8. Heurck, Henri van. A Treatise on the Diatomaceae . Trans. by W.E. Baxter.

    London, Wesley, 1896.

    9. Hustedt, F. “Diatomeen aus der Umbegung von Abisko in Schwedisch-Lappland,”

    Archiv für Hydrobiol. Vol.39, pp.82-174, 1942.

    10. Karsten, Gustav. “Diatomeae,” Engler, Adolf, and Prantl, K. Die

    Natürlichen Pflanzenfamilien . Leipzig, 1928. Vol.2.

    11. Lindemann, E. “Peridineae (Dinoflagellatae),” Naturl. pflFam., 2 aufl.,

    vol.2, pp.3-104, 1928.

    12. Pascher, A. “Heterokonten,” Rabenhorst’s Krypt. -Flora Deutschl . Vol.11,

    pp.1-1092, 1937-9.

    13. Ross, Robert. “Freshwater Diatomeae,” Polunin, Nicholas, ed. Botany

    of the Canadian Eastern Arctic, Pt.II, Thallophyta and

    Bryophyta . Ottawa, 1947. Nat.Mus.Can. Bull. no.97.

    Biological Ser. no.26.

    14. Schiller, J. “Dinoflagellatae (Peridineae) in monographischer Behandlung”

    Ibid. vol.10, no.3, pp.1-617; 1-589, 1931-7.

    024      |      Vol_V-0092                                                                                                                  
    EA-PS. Ross: Algae: Planktoni g c Groups - Bibliography

    15. Shirshov, P.P. “Ecologic-geographical essay on the fresh-water algae

    of Novaya Zemlya and Franz Joseph Land,” Leningrad.

    Arkticheskii Nauchn. - Issled. Inst. Trudy , no.14, pp.73-162,


    16. Fanhöffen, E. “Die Fauna and Flora Grönlands,” Grönland-Exped. Gas.E r R dk.

    Berlin , vol.2, pp.1-383, 1897.

    17. Whelden, R.M. “Algae,” Polunin, N. Botany of the Canadian Eastern Arctic .

    Part II, Thallophyta and Bryphyta , Ottawa, 1947. Nat.Mus.Can.

    Bull . no.97. Biological Series no.26.

    18. Wulff, A. “Ergebnisse der Untersuchung des Oberflächenplanktons,” Ber.Wiss.

    Komm.Meeresforsch. n.f., vol.4, pp.313-37, 1929.


    R. Ross

    Back to top